I know where you can find a few pounds of Pu-238. It's in a graphite cask that ought to be no more than a little singed around the edges.

Oh, and it's located under some 7 miles of ocean, near (perhaps in) one of the deepest ocean trenches in the southwest Pacific. And it's been lying on the ocean floor for a little more than 38 and a half years. So, I guess maybe it might be a little more depleted than we'd want, eh?

-the other Doug

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“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain

I know where you can find a few pounds of Pu-238. It's in a graphite cask that ought to be no more than a little singed around the edges.

The other Doug..................I could have sworn there is another "broken arrow" from the early 1960's that fell from an bomber into a marsh off of Georgia or the Carolinas and still has not been found, someone posted above that weapons grade plutoniem is the "wrong kind" for RTG's. I had suggested in a post above blending the weapons grade stuff with the RTG plutonium to strech the supply to make possible the argo mission....................................

and there are a few sunken soviet and american subs out there that Howerd Hughes falled to retrieve complete with fueled reacters

Oh, this isn't a bomb, it's not weapons-grade Pu. It's RTG-grade. It wasn't launched in an RTG, though -- it would have been transferred into an RTG at its destination. It just never got to its destination.

-the other Doug

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“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain

ISTR reading about RTG powered cable taps*, but "would have been transferred into an RTG had it reached it's destination" suggests that's not it. Aargh! Must know the truth!! I stumbled over this story about RTG-grade Pu production restarting, though; presumably nothing came of it (?)

Actually, while I was mostly kidding about any attempt to find and salvage the Apollo 13 RTG fuel cask, it occurs to me that the only really huge factor against such an undertaking is the rather large portion of ocean floor you'd have to comb trying to find a cask that's less than a meter long and less than 30cm in diameter. There wasn't much tracking of the LM for the last 15 minutes or so before it hit the atmosphere, and the random break-up of a tumbling LM could have imparted a wide variety of different vectors to the cask as it separated from the vehicle.

The other factor that makes it less useful to try and recover such a resource would be the fact that it was produced a good 40 years ago, now, and has been sitting in its current location, in its current form (a rod about 35 to 40cm long and about 5cm in diameter) for the aforementioned 38.5 years. While I imagine it could be further refined to separate out the remaining Pu-238 from the decay products, that process would look a lot like the original production process, wouldn't it? A production process that's shut down for now.

However, if that Pu-238 was in a known location, and if it would be useful for future RTGs, we have the technology to retrieve it. And I bet that the retrieval costs would be less than (or at worst comparable to) the cost of producing the same amount from scratch. And, of course, if you don't have the means of producing more, then the comparison becomes a divide-by-zero error...

Seriously, I know that the ALSEP RTGs had all run down far enough by the time an attempt was made to re-start them in the '90s that none of the five stations responded (assumedly because the power levels had dropped to the point that the transmitter/receivers had shut themselves down). Just how useful would a 40-year-old Pu-238 rod be for future RTGs?

-the other Doug

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“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain

With a radioactive half-life of 87.7 years, you'd have about 73% left after 40 years.llion

Using the production cost of $1.5 billion for 330 pounds (quoted in the link) yields a cost of ~$4.5 million / pound or ~$10 million / Kg. The SNAP-27 RTG in ALSEP contained about 3.8 Kg. 73% of 3.8 Kg is about 2.8 Kg or ~$28 million worth. My SWAG is that the cost of the search and recovery operations will exceed that amount. That is for an amount that will fuel one and only one ASRG.

I wonder how far you can go by just reducing the size/output of the (AS)RTG and putting bigger/better modern batteries in place. For a one day flyby period you could run everything off one decent charge, plus ongoing RTG output - then charge up again for the last look back - with modern memory capacity you can store everything for comms much later. I would guess the limit would be when there is not enough heat from the RTG (direct, or indirect through heaters) to keep the instruments/electronics alive during cruise.Going back to ARGO, is there any possible mission profile that also allows Uranus as well as Neptune? Or is Eris available as a KBO target?

I wonder how far you can go by just reducing the size/output of the (AS)RTG and putting bigger/better modern batteries in place. For a one day flyby period you could run everything off one decent charge, plus ongoing RTG output - then charge up again for the last look back - with modern memory capacity you can store everything for comms much later. I would guess the limit would be when there is not enough heat from the RTG (direct, or indirect through heaters) to keep the instruments/electronics alive during cruise.Going back to ARGO, is there any possible mission profile that also allows Uranus as well as Neptune? Or is Eris available as a KBO target?

The Stirling RTG's use about a quarter (as I recall, please correct if necessary) the plutonium of an MMRTG for the same power output. The plan is to fly two Stirling RTG's per mission. These are mechanical devices (moving piston) so you want a spare.

Uranus is not possible. Don't know if Eris would be in the targetting window for Argo, but Eris is ~3X the distance of Pluto from the sun. That's a long time to ask a spacecraft to survive.

The slides in the March OPAG presentation showed MMRTG with 3.52 Kg and ASRG with 0.88 Kg of Pu-238, so one-fourth the amount is correct. However, the MMRTG electrical output is shown as 123 W vs 140-160 W for ASRG, so ASRG has slightly higher electrical output for the one-fourth amount of Pu-238.

Uranus is not possible. Don't know if Eris would be in the targetting window for Argo, but Eris is ~3X the distance of Pluto from the sun. That's a long time to ask a spacecraft to survive.

Eris seems to be in the right sort of area, and its no further than Voyager is now - heck, if its possible they should go for it. Just call it the "post Neptune interstellar mission" - to probe the heliopause/bow shock - if it gets to Eris, thats a bonus. After all, it is the tenth planet..

As for Uranus, are you sure there is no mission profile? Pioneer 11 did a very sharp turn at Jupiter to get to Saturn. Is the later Jupiter-Uranus-Neptune profile possible? Oh, and then Eris..

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